feat(hook-manager): add Step P.3b eval suite for hook-manager shim skipping (#1838 follow-up) #1891

What should happen

Add behavioral eval coverage in tools/skill-evals/evals/setup-isolated-setup-install/ for Step P.3b (Step-P prose) verifying that the agent skips copying shims to ~/.claude/bin/ for hook managers whose install strategy is none (simple-git-hooks, cargo-husky, git-code-format-maven-plugin, git-build-hook) and installs the shim exclusively for managers requiring an install fix (prek).

To ensure incremental review and zero external tool dependencies, this follow-up is structured into two parts:

• Part 1 (Immediate PR): Implement the step-hook-manager-shim behavioral eval suite in setup-isolated-setup-install covering positive, negative (none-strategy skipping), mixed, and scope boundary cases.
• Part 2 (Subsequent Follow-Up): Empirical execution of git-code-format-maven-plugin and git-build-hook under the whole-user dispatcher in both main checkout and linked worktrees in an environment with JDK 17+ and Maven 3.9+, allowing documentation to drop the "from upstream source" qualifier.

Why

During the review and merge of PR #1838, maintainer @potiuk noted:

"test_none_strategy_generates_no_shim_case pins that the generated shim has no case for a none adapter. The decision that matters is the install step skipping those adapters, which lives in step-p's prose, so its real coverage would be an eval case for setup-isolated-setup-install. A run of the two Maven plugins under the dispatcher, in the main checkout and a linked worktree, would also let those bullets drop the "from upstream source" qualifier."

The generator test test_none_strategy_generates_no_shim_case pins that tools/agent-isolation/hook-manager-shim.sh contains no case statement for none adapters, but does not test the agent's decision-making during Step P.3b execution. Adding an eval suite pins this behavior against regression.

Which layer

Python package (tools/*/ with pyproject.toml)

Boundary conditions (optional)

• Negative skipping: Repositories using only strategy: "none" adapters (simple-git-hooks, cargo-husky, git-code-format-maven-plugin, git-build-hook) must produce installed_shims: [].
• Positive installation: Repositories using prek must produce installed_shims: ["prek"].
• Mixed repositories: Repositories combining prek with none adapters must selectively install installed_shims: ["prek"].
• Unmanaged repositories: Repositories without hook managers must produce installed_shims: [].
• Non-dispatcher scopes: When the operator selects per-project scope, Step P.3b must be skipped entirely (dispatcher_installed: false, installed_shims: []).

Out of scope (optional)

• Modifying tools/hook-manager/registry.json or existing adapter definitions.
• Running live Java/Maven execution (Part 2).

References (optional)

• Follow-up from PR feat(hook-manager): register managers that need no install fix (#1825) #1838 (feat(hook-manager): register managers that need no install fix (#1825))
• tools/hook-manager/registry.json
• plugins/magpie-setup/skills/isolated-setup-install/step-p-sandbox-allowlists.md (Step P.3b)